JPH0229369Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of application of the invention] The invention relates to a pulverized coal combustion boiler, and in particular,
Using a suitable burner to achieve NOx conversion,
By changing the burner arrangement and combustion conditions,
Regarding low NOx combustion boilers that aim to reduce NOx.

[Prior art]

If coal is used as fuel, the lump coal is crushed by a mill.
A pulverized coal combustion method, in which so-called pulverized coal is pulverized directly from a burner into a furnace and combusted, is widely used in practice. Nitrogen oxides (NOx) generated during pulverized coal combustion are FuelNOx, which is generated when the nitrogen content (N content) contained in coal is oxidized, and
Thermal NOx is generated by the oxidation of nitrogen (N ₂ ) in the combustion air. Coal contains a large amount of nitrogen, around 1%, and accounts for over 80% of the total NOx generated. is FuelNOx. Therefore, fuel NOx is the main focus of NOx countermeasures in pulverized coal combustion, and is being considered by many organizations, but it has not yet been put into practical use. However, by improving the pulverized coal combustion method, low
The involvement of low NOx combustion methods to reduce NOx emissions is being actively promoted. In particular, we focused on the fact that NOx and NOx reducing substances are generated by using the furnace of a boiler as a reactor and setting various pulverized coal combustion conditions, and reducing the generated NOx in the furnace. A combustion method that reacts with a chemical substance and reduces it to _N2 was developed by the Special Publication Show.
No. 55-21922. This invention is a combustion method that is one step ahead of conventional pulverized coal combustion by reducing NOx. This invention is a combustion engine that selects the burner arrangement in the furnace and the distribution ratio of fuel and combustion air to completely burn pulverized coal in the main burner, generate a proportionate amount of NOx, and reduce unburned matter. The secondary burner on the downstream side generates reducing substances (such as NH ₃ ) under incomplete combustion conditions, and the NOx generated in the main burner reacts with the reducing substances to reduce NOx to N ₂ . At the last stream side, only auxiliary air for combustion is injected into the furnace, and the unburned matter generated in the incomplete combustion area of the auxiliary burner is completely combusted, thereby increasing the amount of unburned matter. The aim is to achieve low NOx emissions. However, there are problems as shown below. One is the limited reaction field inside the furnace, where NOx generated in the main burner and _NH3 generated in the auxiliary burner are
In order to react with reducing substances such as, it is necessary to sufficiently promote the mixing of the flames of the two. At the same time, even if mixing is promoted, it is impossible to reduce all the generated NOx to 100% _N2 within the limited residence time in the furnace, and some NOx generated in the main burner is It is discharged as is. The amount of unreacted NOx is greatly affected by the amount of NOx generated from the main burner, and the amount of NOx generated by the main burner is not specified in Japanese Patent Publication No. 55-21922, and the air ratio of the main burner is 1.0 or more. In this case, since the amount of NOx produced is large, there is a concern that unreacted NOx will increase. Second, the amount of pulverized coal burned from the main burner and the auxiliary burner is unclear, and if the amount of fuel in the auxiliary burner is large, the air ratio in the auxiliary burner is 1.0.
In order to carry out combustion under the following air shortage conditions, there is a large amount of unburned matter, which is combusted by the auxiliary combustion air jetted out on the downstream side. When this unburned content is combusted, the nitrogen content remaining in the unburned content is oxidized and CharNOx is generated without any countermeasures being taken and discharged. The amount of CharNOx produced depends on the amount supplied from the auxiliary burner, so the amount of CharNOx emitted from the furnace
The amount of NOx can no longer be ignored. Furthermore, the increase in unburned matter from the auxiliary burner is promoted by mixing with auxiliary air, and depending on the mixing conditions, the amount of unburned matter discharged increases, leading to a decrease in combustion efficiency.

[Purpose of invention]

The purpose of this invention is to use the inside of the furnace as a reactor to reduce unburned emissions and effectively reduce
The purpose of the present invention is to provide a low NOx combustion boiler that can achieve NOx reduction.

[Summary of the idea]

This invention divides pulverized coal into two parts, pulverized coal and primary air from the center, and pulverized coal and secondary air from the outer periphery.
Furthermore, we used a low NOx burner with a structure that blows out combustion auxiliary air from the outer periphery. In the main burner, the air ratio is 1.0 or more to reduce unburned content and reduce NOx.
In addition to reducing the concentration, the amount of pulverized coal supplied from the main burner is greater than the amount supplied from the auxiliary burner, so that the auxiliary burner performs low air ratio combustion with an air ratio of 1.0 or less, and the pulverized coal is generated from the main burner. low
Select the air ratio that will generate the amount of reducing substances necessary to reduce the NOx concentration. Under this condition, the air ratio is relatively close to 1.0, and the amount of unburned matter produced is lower than that of conventional technology, and at the same time, the amount of pulverized coal supplied is smaller than that of the main burner, so the total amount of unburned matter can be reduced. Can be done. Therefore, CharNOx generated in the unburnt combustion region in the final stage can be reduced, the amount of unburnt emissions also reduced, and NOx reduction can be effectively achieved while maintaining high combustion efficiency.

[Example of idea]

Embodiments of the present invention will be described in detail below with reference to FIGS. 1 to 7. FIG. 1 shows a schematic diagram of a low NOx burner used as the main burner, which is one of the inventions. This burner is formed from a cylindrical shape. The center nozzle 1 is a heavy oil injection nozzle for ignition. The pulverized coal is divided into two parts and ejected from a nozzle 3 provided on the outer periphery of the central nozzle 1 and a nozzle 4 formed in a ring shape on the outer periphery. Furthermore, a tertiary air nozzle 7 is arranged on the outer periphery. The pulverized coal and air ejected from the nozzle 3 are referred to as primary fuel and primary air, and the pulverized coal and air ejected from the nozzle 4 are referred to as secondary fuel and secondary air. The characteristics of this burner are as follows.
As shown in Fig. 3. As is clear from FIG. 2, the lowest NOx reduction can be achieved by setting the secondary fuel ratio (=secondary fuel/total fuel) to 0.5, that is, by supplying the primary and secondary fuels in equal parts. Figure 3 shows the amount of unburned ash in the combustion ash relative to the total air ratio when fuel is supplied equally based on the results in Figure 2, and the amount of primary air is set to 0.2 relative to the primary fuel. This shows the relationship, and it can be seen that by burning the secondary fuel under the condition that the air ratio≫1.0, the amount of unburned matter is extremely small. Also, as shown in Figure 2, the reason for the low NOx reduction is that the primary fuel is burned at an air ratio of about 0.2, which is one of the reducing substances, as shown in Figure 4. This is because a large amount of NH ₃ is generated, which reacts with NOx generated by the combustion of secondary fuel and can reduce NOx to N ₂ . In particular, in order to simultaneously generate reducing substances such as NH ₃ and NOx in a primary flame and a secondary flame, and the secondary flame to form a flame swirled by the swirler 5 shown in FIG.
Since reducing substances such as NH ₃ and NOx can be actively mixed on the flame trail side, NOx reduction can be effectively achieved.

Next, the determination of the amount of pulverized coal to be distributed from the main burner and the auxiliary burner will be explained with reference to FIG. In pulverized coal combustion, this is caused by the nitrogen content in the coal.
As mentioned above, FuelNOx accounts for most of the total NOx, but FuelNOx is further classified into VolatileNOx, which is generated when volatile matter is burned, and CharNOx, which is generated when the fixed component, char, is burned.
Figure 5 shows the results of measuring the generation ratio of VolatileNOx and CharNOx, and the experiment was conducted using a fully premixed burner that mixes the entire amount of pulverized coal and combustion air beforehand. . As a result, most of FuelNOx is VolatileNOx,
It became clear that CharNOx cannot be ignored in order to achieve low NOx reduction. That is, the fuel split burner shown in FIG. 1 is used as the main burner, and the amount of pulverized coal supplied is larger than that of the auxiliary burner. This reduces the combustion amount of the auxiliary burner, and the auxiliary burner
As shown in the figure, in order to generate reducing substances such as NH ₃ to reduce NOx generated in the main burner, the air ratio needs to be 1.0 or less. This combustion condition also increases the unburned content in the ash, but since the absolute amount of pulverized coal is smaller than that of the main burner, the amount of unburned content can also be reduced. Moreover, since the concentration of NOx generated from the main burner is low, the combustion conditions in the auxiliary burner can be such that combustion can be performed in a region where the air content is close to 1.0, and unburned matter can also be kept relatively low. Therefore, the supply distribution of pulverized coal is more effective as the number of main burners is greater than the number of sub-burners.

Next, as a ripple effect of reducing the amount of combustion from the auxiliary burner, the absolute amount of CharNOx can also be reduced, as shown in FIG. Moreover, this also facilitates complete combustion of unburned matter in the final region.

Next, the individual features explained above will be summarized, and one embodiment of the low NOx boiler of the present invention will be described with reference to FIG. The main burner 9 is the lowest stage (most upstream side) of the furnace 8
An auxiliary burner 10 is placed on the downstream side, and a combustion auxiliary air jet nozzle 11 is placed on the downstream side. In this embodiment, a front firing boiler is taken as an example. Further, a plurality of main burners 9, sub-burners 10, and nozzles 11 were arranged. The main burner 9 is a fuel split type low burner shown in Figure 1.
A NOx burner was used, and the auxiliary burner 10 was a two-stage combustion type burner. In the main burner 9, a mixed flow 12 of primary fuel and primary air is ejected from the center nozzle, a mixed flow 13 of secondary fuel and secondary air is ejected from the outer nozzle, and tertiary air 14 is ejected from the outer nozzle to create a combustion flame. Form A. Flame A is a primary flame that generates reducing substances in an air-starved state, and the secondary flame generates NOx, both of which can proceed independently at the same time.
can be reduced to N ₂ to reduce NOx. Therefore, combustion gas containing a low concentration of NOx from flame A contacts and mixes with flame B from the auxiliary burner. The auxiliary burner 10 is supplied with a mixed flow 15 of pulverized coal and primary air and auxiliary air 16 for combustion, and the total amount of primary and secondary air is equal to or less than the theoretical combustion air amount of pulverized coal. Form B. As mentioned above, in the flame B, almost no NOx is generated, and reducing substances are generated, so that the NOx generated in the main burner can be reduced to N ₂ by mixing with the flame B. In addition, since unburned matter is generated in the flame B, the combustion auxiliary air 17 is supplied to the nozzle 1.
1 into the furnace 8, a combustion flame C of the unburned matter generated in the flame B is formed, and countermeasures against the unburned matter are implemented in the final combustion region.

Based on the configuration shown in FIG.
60%, 40% from the auxiliary burner 10, and the total air ratio λ ₁ = 0.9 to 1.2 in the main burner 9, the total air ratio λ ₂ = 0.8 to 0.9 in the auxiliary burner 10, and from the nozzle 11 into the furnace 8. As a result of ejecting and burning combustion air 17 corresponding to an air ratio λ ₃ = 1.3 with respect to the amount of pulverized coal in the total fuel supplied, the NOx at the furnace outlet was 80 to 100 ppm, and the unburned content was 2 to 3%. Ta. These test results show the lowest NOx = λ ₁ = 1.0, λ ₂ = 0.9, and λ ₃ = 1.3.
A value of 80ppm has been obtained.

Although the present invention has been described above with respect to a front-firing combustion boiler, similar effects can be obtained with a facing combustion boiler.

In addition, in the figure, 2 is a primary fuel supply pipe, and 6 is a tertiary air supply pipe.

[Effect of idea]

According to this invention, while maintaining high combustion efficiency,
Ultra-low NOx levels of 100 ppm or less can be achieved, and the ripple effect is that the flue gas treatment process can be simplified, such as by eliminating the need for conventional flue gas denitrification equipment.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the low NOx burner of the present invention, Figures 2 and 3 are characteristic diagrams of the burner in Figure 1, and Figure 4 shows the relationship between NOx and one of the reducing substances in the low air ratio region. A certain NH ₃ production characteristic diagram, Figure 5 is a breakdown diagram of Fuel NOx, and Figure 6 is an overall configuration diagram of the present invention. 9...Main burner, 10...Sub-burner, 11...
Air nozzle, 12...Mixed flow of primary fuel and primary air, 13...Mixed flow of secondary fuel and secondary air.

Claims (1)

[Scope of claim for utility model registration] A plurality of main burners located at the most upstream side with respect to the flow direction of combustion gas in a pulverized coal combustion boiler, a plurality of auxiliary burners located in the middle stage, and combustion air further upstream. The NOx produced by the main burner is reduced by the reducing substance produced by the auxiliary burner, and the unburned matter is combusted by the air ejected at the final stage. The main burner is concentric, with a supply nozzle for pulverized coal and primary air in the center, and swirl vanes on the outer periphery adjacent to this, and a supply nozzle for supplying pulverized coal and secondary air in an amount capable of forming a flame. A low NOx combustion boiler characterized by comprising a supply nozzle, and a nozzle on its outer periphery that spouts only combustion air.